在意外放电时形成的准晶体

诸平

Fig. 1 Cross-section of a fulgurite sample showing fused sand and melted conductor metal from a downed powerline. Credit: Luca Bindi et al

Fig. 2 Diffraction pattern of a quasicrystal showing 12-fold symmetry. Credit: Luca Bindi et al

据美国物理学家组织网（Phys.org）2022年12月30日报道，来自意大利佛罗伦萨大学（Università di Firenze）、美国南佛罗里达大学（University of South Florida）、美国加州理工学院（California Institute of Technology）和美国普林斯顿大学（Princeton University）的一组研究人员发现，在一次意外放电中形成了准晶体（Quasicrystal formed during accidental electrical discharge）。相关研究结果于2022年12月30日已经在《美国国家科学院院刊》（Proceedings of the National Academy of Sciences简称PNAS）杂志网站发表——Luca Bindi. Matthew A. Pasek, Chi Ma, Jinping Hu, Guangming Cheng, Nan Yao, Paul D. Asimow, Paul J. Steinhardt. Electrical discharge triggers quasicrystal formation in an eolian dune. Proceedings of the National Academy of Sciences, December 27, 2022, 120 (1): e2215484119. DOI: 10.1073/pnas.2215484119. https://doi.org/10.1073/pnas.2215484119

在此论文中，该小组描述了他们对美国内布拉斯加州（Nebraska）一个沙丘（sand dune）中发现的准晶体（Quasicrystals）的研究。

准晶体，顾名思义，是类似晶体的物质。它们具有在普通晶体中不存在的特征，例如原子的不重复排列。到目前为止，准晶体已经被发现嵌在陨石和核爆炸的碎片中。在这项新的研究中，研究人员在内布拉斯加州的沙丘（Sand Hills, Nebraska）中发现了一个准晶体嵌入在其中。

对准晶体的研究表明，它具有12倍或十二方对称性（12-fold, or dodecagonal, symmetry），这在准晶体中很少见。由于好奇它是如何形成的，以及它是如何在沙丘中结束的，研究人员做了一些调查。他们发现一根电线落在了沙丘上，很可能是雷击造成的。他们认为，来自电线或闪电的电涌可能产生了准晶体。

研究人员指出，准晶体是在一个管状的电闪石（fulgurite）中发现的，他们认为这也是由于电线上熔化的沙子和金属熔合而在电涌期间形成的。

在使用电子显微镜（electron microscope）观察准晶体时，研究人员能够分辨出它的组成。在这样做的过程中，他们发现了二氧化硅玻璃碎片，这告诉他们，放电期间沙丘内部的温度至少达到了1710 ℃。他们还发现准晶体是从熔化的铝合金（aluminum alloy）和硅酸盐玻璃之间的过渡区域提取出来的。他们的工作证实了他们正在研究的物体确实是一种准晶体，而且它具有以前未见过的成分。

研究人员得出结论，在这样的地方发现准晶体表明，其他的准晶体也可能是由于雷击或电线倒塌而形成的。他们还表示，他们的工作可能会导致在实验室中创造准晶体的技术。

本研究得到了MIUR-PRIN2017资助（MIUR-PRIN2017, project “TEOREM—deciphering geological processes using Terrestrial and Extraterrestrial ORE Minerals,” prot. 2017AK8C32），也得到了美国普林斯顿大学自然科学新理念创新基金（Princeton University Innovation Fund for New Ideas in the Natural Sciences）以及美国国家科学基金会(NSF, award 1725349)的部分支持。

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Newly discovered quasicrystal was created by the first nuclear explosion at Trinity Site

Significance

The article presents the quasicrystal created by an electrical discharge, in this case accidentally created by a lightning strike or a downed power line in a wind-created dune in the Sand Hills of north central Nebraska. The discharge produced extreme temperatures (>1,710 ℃) that led to the formation of a fulgurite, a tube of fused and melted sand along with traces of melted conductor metal from the power line. Within the fulgurite was found a “dodecagonal quasicrystal” composed of equally spaced atomic layers, each with 12-fold symmetry and quasicrystalline order that is impossible for ordinary crystals. The discovery suggests mechanisms for forming quasicrystals in nature (on Earth and in space) and in the laboratory.

Abstract

We report the discovery of a dodecagonal quasicrystal Mn_72.3Si_15.6Cr_9.7Al_1.8Ni_0.6—composed of a periodic stacking of atomic planes with quasiperiodic translational order and 12-fold symmetry along the two directions perpendicular to the planes—accidentally formed by an electrical discharge event in an eolian dune in the Sand Hills near Hyannis, Nebraska, United States. The quasicrystal, coexisting with a cubic crystalline phase with composition Mn_68.9Si_19.9Ni_7.6Cr_2.2Al_1.4, was found in a fulgurite consisting predominantly of fused and melted sand along with traces of melted conductor metal from a nearby downed power line. The fulgurite may have been created by a lightning strike that combined sand with material from downed power line or from electrical discharges from the downed power line alone. Extreme temperatures of at least 1,710 ℃ were reached, as indicated by the presence of SiO₂ glass in the sample. The dodecagonal quasicrystal is an example of a quasicrystal of any kind formed by electrical discharge, suggesting other places to search for quasicrystals on Earth or in space and for synthesizing them in the laboratory.